Field of the Invention
The present invention relates to a wireless charging coil PCB structure, more particularly to a wireless charging coil PCB structure for overcoming the proximity effect between coils.
Description of the Prior Art
Wireless Charger (WLC) is a cordless power transmission technology using electromagnet induction. FIG. 1 is a schematic diagram showing the wireless charging scheme. The shown wireless charging scheme comprises a power transmitting module 10 and a power receiving module 20. The power transmitting module 10 comprises a transmitting-end coil 11 and a transmitting-end ferrite plate 12. The power receiving module 20 correspondingly comprises a receiving-end coil 21 and a receiving-end ferrite plate 22. When the power receiving module 20 is in proximity of the power transmitting module 10 and electrical current flows through the transmitting-end coil 11 to generate magnetic field, the receiving-end coil 21 of the power receiving module 20 will generate electrical current induced by the magnetic field.
The high end WLC module has plate with larger size at the power transmitting-end such that the power receiving module can be successfully charged as long as it is close to the plate of the power transmitting-end. Therefore, the power transmitting module will arrange lots set of coils to cover the desired charging range. For example, two sets of coils, or even three sets of coils may be arranged.
The turn number and the coil inductance are related to the transmitting frequency of wireless charging and a non-coil region is formed at the center of the coil, therefore, another set of coil is generally arranged on the top of one set of coil. FIG. 2 shows the schematic view of a prior art inductor plate 12 with two sets of coils, where the coil 11 is arranged on top layer of the inductor plate 12 and another coil 11′ is arranged on bottom layer of the inductor plate 12. Part of the coil 11 on top layer of the inductor plate 12 has a projection on the non-coil region 13′ of the coil 11′ on bottom layer; and part of the coil 11′ on bottom layer of the inductor plate 12 has a projection on the non-coil region 13 of the coil 11 on top layer.
FIG. 3 shows the schematic view of another prior art inductor plate 12 with three sets of coils, and FIG. 4 shows the sectional view of the inductor plate 12 in FIG. 3. The three sets of coils are arranged in three overlapped rectangular manner. Namely, the coil 11′ on top layer of the inductor plate 12 has a projection at the center between two other coils 11″ on bottom layer of the inductor plate 12, and a part of the coil 11′ on top layer of the inductor plate 12 has a projection on the non-coil region 13 of the other two coil 11″ on bottom layer of the inductor plate 12. Similarly, more sets of coils such as four, five or even more sets of coils can be arranged in way similar to those shown in FIGS. 3 and 4, and the detailed description is omitted here for brevity.
In the inductor plate 12 shown in FIG. 4, the stacked coils are generally manufactured with multi-layer printed circuit board to reduce the overall height of the inductor plate 12. The inductor plate 12 for mounting the three coils 11′, 11″ is arranged on a ferrite plate 14 and is covered with a top plate, resulting in a WLC plate structure with at least four layers.
The high-end WLC module has higher demands for transmitting efficiency and heat dissipation ability; therefore, the coil impedance should be accordingly low for the PCB. However, the WLC module uses high frequency alternating current (AC) and the transmitting efficiency is related to the coil frequency and the matching of inductance. Coil impedance will increase and inductance will have fluctuation if proximity effect occurs between coils close to each other or between upper and lower stacked coils. Moreover, heat dissipation effect is also degraded. These are drawbacks to be overcome for high-end WLC module.